The evolution of the low-density H i intergalactic medium from z = 3.6 to 0: Data, transmitted flux, and H i column density

Kim, T-S; Wakker, B P; Nasir, F; Carswell, R F; Savage, B D; Bolton, J S; Fox, A J; Viel, M; Haehnelt, M G; Charlton, J C; Rosenwasser, B E

Abstract

We present a new, uniform analysis of the H I transmitted flux (F) and H I column density (⁠NHI⁠) distribution in the low-density IGM as a function of redshift z for 0 < z < 3.6 using 55 HST/COS FUV (Δz = 7.2 at z < 0.5), five HST/STIS+COS NUV (Δz = 1.3 at z ∼ 1) and 24 VLT/UVES and Keck/HIRES (Δz = 11.6 at 1.7 < z < 3.6) AGN spectra. We performed a consistent, uniform Voigt profile analysis to combine spectra taken with different instruments, to reduce systematics and to remove metal-line contamination. We confirm previously known conclusions on firmer quantitative grounds in particular by improving the measurements at z ∼ 1. Two flux statistics at 0 < F < 1, the mean H I flux and the flux probability distribution function (PDF), show that considerable evolution occurs from z = 3.6 to z = 1.5, after which it slows down to become effectively stable for z < 0.5. However, there are large sightline variations. For the H I column density distribution function (CDDF, f ∝ N−βHI⁠) at log(NHI/1cm−2) ∈ [13.5, 16.0], β increases as z decreases from β = 1.60 at z ∼ 3.4 to β = 1.82 at z ∼ 0.1. The CDDF shape at lower redshifts can be reproduced by a small amount of clockwise rotation of a higher-z CDDF with a slightly larger CDDF normalisation. The absorption line number per z (dn/dz) shows a similar evolutionary break at z ∼ 1.5 as seen in the flux statistics. High-NHI absorbers evolve more rapidly than low-NHI absorbers to decrease in number or cross-section with time. The individual dn/dz shows a large scatter at a given z. The scatter increases toward lower z, possibly caused by a stronger clustering at lower z.

Citation

Kim, T.-S., Wakker, B. P., Nasir, F., Carswell, R. F., Savage, B. D., Bolton, J. S., Fox, A. J., Viel, M., Haehnelt, M. G., Charlton, J. C., & Rosenwasser, B. E. (2021). The evolution of the low-density H i intergalactic medium from z = 3.6 to 0: Data, transmitted flux, and H i column density. Monthly Notices of the Royal Astronomical Society, 501(4), 5811-5833. https://doi.org/10.1093/mnras/staa3844

• Journal Article Type: Article
• Acceptance Date: Dec 10, 2020
• Online Publication Date: Dec 14, 2020
• Publication Date: 2021-03
• Deposit Date: Dec 16, 2020
• Publicly Available Date: Jan 4, 2021
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 501
• Issue: 4
• Pages: 5811-5833
• DOI: https://doi.org/10.1093/mnras/staa3844
• Keywords: Space and Planetary Science; Astronomy and Astrophysics
• Public URL: https://nottingham-repository.worktribe.com/output/5152540
• Publisher URL: https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/staa3844/6033999
• Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record T-S Kim, B P Wakker, F Nasir, R F Carswell, B D Savage, J S Bolton, A J Fox, M Viel, M G Haehnelt, J C Charlton, B E Rosenwasser, The evolution of the low-density H i intergalactic medium from z = 3.6 to 0: data, transmitted flux, and H i column density,,, Monthly Notices of the Royal Astronomical Society, Volume 501, Issue 4, March 2021, Pages 5811–5833 is available online at: https://doi.org/10.1093/mnras/staa3844